This invention concerns sports footwear with studded soles, such as football boots, rugby boots and hockey boots, and particularly relates to novel kinds and arrangements of studs for these.
Conventionally studs are cylindrical or frustoconical projections from the sole. Recently-available designs have non-circular studs in the form of straight or curved fins, or triangles. These are designed to be visually distinctive; they may also affect ground penetration and grip.
Studs may be moulded integrally with a plastic sole unit. It is also known for circular or triangular studs to be fixed detachably by threaded bolts which screw into threaded sockets embedded in the sole. In the latter case the stud body generally has a polygonal portion or other flats for engagement by a spanner.
See e.g. US-A-4590693 and EP-A-815759.
We now disclose new and useful developments in this field as regards the shape and mounting of studs.
Our first proposal relates to studs shaped with non-circular symmetry. We have found that such studs can be designed to tailor the grip properties of the footwear in different directions of foot action, and that the behaviour of a ground surface penetrated by a stud is to some extent fluid, depending on how wet it is, making the horizontally-directed fluid dynamic profile of the stud a significant factor in its behaviour.
Thus the first set of proposals relates to the shape of studs.
For convenience in describing directional studs we shall use the term xe2x80x9cdrive linexe2x80x9d which is a median line (radial, for a rotationally-fastened stud) in the direction of the stud""s maximum flow resistance.
A stud will naturally project the same area in opposite directions along the drive line, but directional properties can be achieved by adjusting the angular presentation of the stud surface relative to the drive line in these two directions. In general terms we propose a directional stud which has one or more relatively abrupt faces presenting a first resistance to movement of the stud in a first radial direction through a flowable ground material at the drive side, facing along the drive line, and a relatively inclined or convergent face or faces on the other side which can be termed the compliant side presenting a second resistance to movement of the stud directed radially oppositely to the first radial direction.
An abrupt face desirably extends substantially parallel to the stud axis, preferably within 10 degrees of parallel, and transverse to the drive line. Preferably it is substantially flat; alternatively it may be recessed relative to its own border (i.e. concave). Desirably such abrupt face accounts for at least 40% or preferably at least 50 or 60% of the total stud area projected along the drive direction in situ.
The compliant side has more inclined face than the drive side to reduce its relative flow resistance. Consequently, the first resistance of the abrupt drive face is greater than the second resistance of the compliant side. Preferably the inclined face is provided as flank regions which diverge in the drive direction towards shoulders where they meet the drive side. The inclined face is preferably inclined to the stud axis, i.e. axially convergent, by at least 30 degrees or 40 degrees. Preferably inclined face is divergent from the drive line by not more than 60 degrees, preferably not more than 50 degrees. Such surface may be flat, or more preferably concave as discussed further below. Preferably it is generally smooth to improve flow.
Desirably such inclined face accounts for at least 50% or preferably at least 60% or 70%, of the total stud area projected along the reverse of the drive direction in situ. Indeed, inclined face having one or both of axial convergence and plan divergence may account for upwards of 80% of that area.
Preferably divergent flank regions on the compliant side lead to shoulders of the abrupt face on the drive side. For a combination of ground penetration with suitable face inclination it is preferred that the flank regions and the shoulders, preferably also a median ridge where the flank regions meet, are axially convergent as specified above. Any one and preferably all of these axially convergent features is/are desirably also concave in axial section. This keeps down the ratio of the radial cross-sectional area relative to the penetrant area of drive face at a given depth.
Providing axial convergences and face inclinations relative to the direction transverse to the drive line enables the stud to become relatively compliant in that direction too. This lateral compliance can help to reduce leg injuries associated with undesirable stud resistance to sideways and twisting movements of the foot. For football, a forward inclination of the stud also reduces difficulties in getting the toe down under the ball for kicking.
A particularly preferred form of stud has a shaped stud body, preferably a plastics moulding, penetrated by an axial securing bolt whose drive head is exposed at the top of the stud and whose threaded end projects below a base plane of the stud. The stud body has a generally flat drive face on the drive side, substantially perpendicular to the horizontal drive line. The flat drive face is bordered at the sides by lateral shoulders which converge towards the top of the stud body, preferably at least 30 degrees relative to the axial direction overall from the base to the top of the stud body, and which preferably are concave. On the compliant side the stud has divergent flank faces diverging from a median ridge at their meeting to the respective shoulders, and which converge axially towards the top of the stud body as does the median ridge. Convergence to the top of the body is preferably at least 40 degrees (overall from top to bottom) relative to the axial direction. Preferably the median ridge and most preferably also the flank faces are concave at least in axial planes and, for the faces, also in radial planes.
A second independent aspect of our proposal relates to studs releasably securable to the sole by engagement of a rotational fastener portion of the stud with a complementary rotational fastener portion of the sole, e.g. screw-threaded portions. In addition to its fastener portion the foot of the stud has a stud alignment formation, extending off-axis and engageable to overlap axially with an alignment formation of the sole to hold a predetermined rotational orientation of the stud relative to the sole when securing the stud.
Preferably the rotational fastener portion of the stud is rotatable relative to the stud""s alignment formation. The fastener components can then be rotated to a secure or tight condition after the stud is locked at the desired orientation. For this purpose an axial freedom of movement of the stud""s fastener portion relative to the alignment portion is also desirable, making it easier to move the alignment portion into engagement after initially engaging the fastener, or vice versa.
The stud""s fastener portion is conveniently an axial bolt, e.g. a threaded bolt, projecting below the foot of the stud body. The stud""s fastener portion may be a discrete component housed in a stud body component, e.g. a metal fastener housed in a moulded plastics stud body since this corresponds closely to familiar constructions. A drive head for the fastener portion of engagement by a fastening tool, e.g. a hexagonal or other polygonal head, may project from or be exposed at the top of the stud body.
The alignment formations may be chosen from a wide range of possibilities, provided that when engaged (with an axial overlap) they prevent rotation of the stud in at least one and preferably both rotational senses. However we note a number of criteria leading to preferred constructions. For ease of manufacture and durability, the alignment formations on the stud and/or sole are desirably fixed, integral formations e.g. moulded in one piece. There may be for example one or more localised projections or lugs on one component engageable in one or more corresponding recesses, preferably substantially complementary in shape, on the other. Preferably a projection is on the stud body and a recess on the sole, since projections are more susceptible to damage and the stud is more easily replaced. It is also possible to have the recess on the stud and a projecting lug on the sole. It may also be desired to allow conventional flat-bottomed studs to be used on the same sole; a projection on the sole might hinder this.
Alternatively the stud""s foot as a whole may be eccentric or non-circular in some respect and sit bodily in a complementary or at least rotation-inhibiting recess of the sole.
Preferably the alignment formations lock a unique rotational orientation, but in some contexts it may desired to provide multiple rotational symmetry so that there are two or more lockable orientations.
The resultant ability to ensure a predetermined rotational orientation of a stud may be useful for a variety of functional and/or aesthetic reasons for studs which in some respect lack full circular symmetry. We particularly envisage its use for studs shaped to have higher flow resistance in one radial direction than in a transverse radial direction e.g. elongate fin shapes, (perhaps with two-fold symmetry), or than in the opposite radial direction (e.g. triangular shapes, and/or shapes with substantially one-fold or three-fold symmetry). In particular it may be used in conjunction with the first aspect discussed previously.
A third independent aspect of the present proposals, which may be used in conjunction with the first and/or second aspects above, relates to the disposition of directional studs on the sole of the footwear.
As to the number of studs, this may be in accordance with conventional layouts. Thus, the total number of studs is typically from 4 to 12. There may be from 3 to 8 studs in the forefoot region and 2 to 4 studs in the rearfoot (heel) region, usually with a stud-free area at the instep.
The forefoot plays the major part in forward drive and turning; while sprinting the rearfoot makes little significant contact with the ground. The rearfoot is important in slower running when the foot lands and when slowing down. It is desirable as part of the xe2x80x9cbraking phasexe2x80x9d of running and to minimise slipping of the relevant part of the foot. Thus, we propose firstly that most or all of the directional studs of the forefoot or first part of the sole (which may be a majority or all of the studs of the forefoot) have the drive side facing rearwardly or towards a second part of the sole. Conversely, most or all of the directional studs (generally a majority or all of the studs) at the rearfoot or second part of the sole have the drive (high-resistance) side directed forwards or towards the first part of the sole.